Gaskets and seals perform the primary function of preventing the flow of fluids past moving or stationary mechanical interfaces. Gaskets are normally employed with stationary interfaces. The normal requirements for gaskets as set forth in the Handbook of Mechanical Packings and Gasket Materials published by the Mechanical Packing Association, New York, New York, include mainly low creep, resistance to chemical attack and conformability. While many gasket materials are available, none has been developed that satisfies all of these requirements to the degree that is desired in commercial practice. It is particularly difficult to combine low creep and high conformability. Elastomeric materials that conform well to rough surfaces, tend to creep under high pressures. Metal gaskets, in the other extreme, resist high pressure creep, but have poor conformability. Also, they are very susceptible to corrosion.
Seals commonly prevent the flow of fluids past sliding mechanical interfaces, such as rotating shapes, and have additional requirements over and above those of gaskets. Seals must have resistance to wear and must possess a low coefficient of friction. Another requirement in many seal applications is porosity which is essential to retain fluid lubricants. In such applications there is the need to retain this porosity under compression. Of the many seal materials available, including packing materials, none satisfactorily meets all requirements desired in commercial practice.